Light-ish tent for weeks in the sun over years?

What do they use on yurts? Vinyl laminate of some sort.

Yurts do seem to last quite a while in the sun.  So do hot tub covers – kind of a naugahyde-like material.

Cheaper than either would be the covers on free-standing car-ports:

Or those pop-up sun shades seen at farmers’ markets, etc:

Some of which come with sides.  Not light, but cheap, great headroom, and they seem to last a long time.

A tarp over a tent could be the lightest economical solution.

Any cheap tarp will do, change that every season or when needed.

I think Franco is right, unless the tent needs to be some unusual shape or size or has to not be ugly. Anything exposed to the sun that much is going to age hard and a semi-sacrificial buffer layer seems like a good idea.

BTDT and I agree with Franco; although having a substantial frame as with the portables works well

If the weather is hot there will be advantage in using a much more open weave fly too, in which case I have argued in the past for using cheap poly/cotton bed sheeting or shade cloth

Tyvek 1443R could do here.

Works well as a “shade cloth” , light, easy to work with and cheap enough.

Obviously not stealth but if something like that is required should be spelled out at the start.

Yeah, Tyvek.  They make RV covers out of it.  Similar application.

Either make a tent out of it, or make a cover for your tent

Polyester fabric lasts longer than nylon.  Like the RSBTR silpoly.  You might have to replace it after a few years.  I have some polyester rope that I put up all summer and after several years I can see how it’s degrading.  Might throw it out this year.

Dark colored, silicone coated polyester will be your best bet for lightweight with good UV resistance (for a single layer fabric).

When we went hot air ballooning in Albuquerque NM, I talked to the guy (our captain?) about the fabrics, and he said that the black and dark blue colored nylon fabrics lasted longer in the sun than other colored nylons.

Aluminized cuben would work very well, but it’s pricey and hard to find.

(Some Tyvek products are treated to have better UV resistance, but the base material–HDPE–innately has poor UV resistance).

If the shade cloth is touching or just a foot or so above the tent, the tent will get hotter under a dark colour.